1. Field of the Invention
The present invention relates to a geomagnetic sensor and a method for measuring an azimuth angle using the same, and more particularly, to a geomagnetic sensor which informs a user that an error might be present in the azimuth angle information being currently measured upon determination that there is a change in a circumferential magnetic field environment, and a method for measuring the azimuth angle using the same.
2. Description of the Related Art
A geomagnetic sensor operates to measure intensity and direction of a terrestrial magnetism which a human can not perceive, and in particular, a sensor which operates to measure the geomagnetism using a fluxgate is called a fluxgate type geomagnetic sensor.
The fluxgate type geomagnetic sensor employs as its magnetic core a material such as a permalloy having a high permeability, wherein an exited magnetic field is applied through a driving coil which is wound on the core to measure secondary harmonic components proportional to an external magnetic field generated in response to the magnetic saturation and the non-linearity magnetic characteristics of the core, thereby allowing the intensity and the direction of the external magnetic field to be measured.
Such a fluxgate type was developed in the late 1930s, and provides several advantages such as it has an economical property, a good sensitivity, and can be relatively small-sized as compared to other kinds of geomagnetic sensors. In addition, it also has advantages in that it consumes less power and provides a long-term stability of its output signal, so that it is widely employed for civilian and military purposes ranging from weak magnetic field detection, measurement of terrestrial absolute direction to exploration of a vein of ore, target detection, positional control of an artificial satellite, and space probing, and research for enhancing its performance have been continuously conducted. In particular, since a Micro Electro Mechanical System (MEMS) technique has been gradually developed in recent years, a very small-sized fluxgate type geomagnetic sensor consuming low power by means of the MEMS technique may be fabricated, and is also built in various portable electronic devices such as a mobile phone, a Personal Digital Assistant (PDA), a notebook, a Personal Computer (PC) or the like.
FIG. 1 is a schematic diagram showing an internal configuration of a typical geomagnetic sensor including two axis fluxgates for detecting geomagnetism. Referring to FIG. 1, the geomagnetic sensor 10 includes an X-axis fluxgate 11 and a Y-axis fluxgate 13. Each of the X and Y axis fluxgates 11 and 13 has a rectangular or bar-shaped magnetic core, a driving coil which is wound on the core, and a detection coil. The driving coil operates to excite and magnetize the magnetic core by receiving an external electrical signal, and the detection coil operates to detect an electromotive force which is induced from the magnetism generated from the drive of the driving coil.
A control unit (not shown) of the geomagnetic sensor 10 uses both output values of the X and Y fluxgates 11 and 13 to calculate a current azimuth angle by means of predetermined formulae.
FIG. 1 also shows three axes which are references for measuring a pitch angle, a roll angle, and a yaw angle of the geomagnetic sensor 10. The pitch angle and the roll angle indicate rotational angles with respect to a horizontal plane on which the geomagnetic sensor 10 is positioned when the geomagnetic sensor is rotated based on each of two axes thereof. The yaw angle indicates a rotational angle measured when the geomagnetic sensor 10 is rotated around the axis vertical to the plane on which the geomagnetic sensor 10 is positioned.
It is determined that the geomagnetic sensor 10 is inclined at a predetermined angle when at least one angle of the pitch angle and the roll angle of the geomagnetic sensor 10 is not zero degree, so that the output values of the X and Y axis fluxgates 11 and 13 may be distorted due to such an inclination. As a result, the azimuth angle which was calculated using the distorted output values may be distorted.
A tilt compensation algorithm for compensating the inclination effect is known in the related art, however, additional information with respect to the current inclination (the pitch angle, the roll angle), a magnetic dip or the like of the geomagnetic sensor 10 are required in order to carry out the tilt compensation algorithm. As a result, additional hardware, such as an acceleration sensor capable of measuring the pitch angle and the roll angle, is required. Accordingly, such a geomag has difficulty in allowing the sensor to be built in various portable electronic devices which should be implemented in very small-sized shapes.
In addition, when the azimuth angle is measured using the geomagnetic sensor 10 under an environment having a circumferentially strong magnetic field, the information with respect to the distorted azimuth angle may be detected even at a horizontal state (namely, the pitch angle=the roll angle=zero degree).
However, the geomagnetic sensor of the related art is unable to recognize that the azimuth angle information is normal or distorted even when the azimuth angle measured by the related art might be distorted. As a result, a user must determine whether he/she should accept the measured azimuth angle or compensate for the geomagnetic sensor in the current position by determining the azimuth angle again.